But Justice Antonin Scalia, one of the most conservative members of the court, asked how long sodomy had been a crime in Texas, pointing out that legal rights protected by the constitution had be to be well-founded and deeply rooted.

It has had such a statute since 1854 - but in 1973 it changed the law to apply only to same-sex couples.

In the case being considered by the court, two men, John Lawrence and Tyron Garner, were arrested after a neighbour falsely reported that a man with a gun was "going crazy" in Mr Lawrence's apartment.

The neighbour was convicted of filing a false report, but Mr Lawrence and Mr Garner were arrested, jailed overnight, and fined $200 each plus court costs.

Broader issue

In addition to gay-rights campaigners, the two men are being supported by some conservative and libertarian groups that argue the government should not interfere in citizens' sexual lives.

Texas has the support of conservative religious groups and three other states - Alabama, South Carolina and Utah.

In last four decades, the US Supreme Court has established a right of privacy that extends to a range of sexual conduct - including the right to contraception and abortion, even for unmarried couples.

Justices Stephen Breyer and Ruth Bader Ginsberg, in particular, asked how the state of Texas could justify allowing homosexual couples to adopt children and raise a family, yet ban their sexual practices.

But the state of Texas argued strongly that in matters of morals, the state legislature should have the right to decide what standards should apply in the community.

"Twenty-three million Texans are asking for the right to participate in decisions on moral issues," Mr Rosenthal said.

In recent rulings, particularly ones relating to sentencing, the Supreme Court has granted increasing discretion to states to make their own decisions.

So this case could be central in defining the end of a era of social activism by the Court that reshaped America.

Options for decision

The Supreme Court has a number of options in deciding the case:

It can rule that the Texas law is constitutional

It can rule that the law unfairly discriminates against homosexuals - meaning that states can ban certain sexual activity as long as it bans it for everyone, heterosexual and gay alike

It can reverse its 1986 decision, Bowers v Hardwick, essentially ordering the government out of the bedroom in the case of consensual sex between adults

Three of the nine judges who were on the court in 1986 are still there today.

Chief Justice William Rehnquist and Justice Sandra Day O'Connor voted with the majority. Justice John Paul Stevens dissented.

The late Lewis Powell, who cast the deciding vote in the 5-4 1986 ruling, later said the losing side had the stronger case.